Glyoxal crosslinked cellulosic fibers having improved brightness and color

ABSTRACT

Glyoxal crosslinked cellulosic fibers having improved brightness and color, and methods for making the fibers.

FIELD OF THE INVENTION

The present invention relates generally to cellulosic fibers and, morespecifically, to glyoxal crosslinked cellulosic fibers having improvedbrightness and color.

BACKGROUND OF THE INVENTION

Cellulosic fibers are a basic component of absorbent products such asdiapers. The ability of an absorbent product containing cellulosicfibers to initially acquire and distribute liquid will generally dependon the product's dry bulk and capillary structure. However, the abilityof a product to acquire additional liquid on subsequent insults willdepend on the product's wet bulk. Cellulosic fibers, although absorbent,tend to collapse on wetting and to retain absorbed liquid near the pointof liquid insult. The inability of wetted cellulosic fibers in absorbentproducts to further acquire and distribute liquid to sites remote fromliquid insult can be attributed to a diminished acquisition rate due inpart to the loss of fiber bulk associated with liquid absorption.Absorbent products made from cellulosic fluff pulp, a form of cellulosicfibers having an extremely high void volume, lose bulk on liquidacquisition and the ability to further wick and acquire liquid, causinglocal saturation.

Crosslinked cellulosic fibers generally have enhanced wet bulk comparedto uncrosslinked fibers. The enhanced bulk is a consequence of thestiffness, twist, and curl imparted to the fiber as a result ofcrosslinking. Accordingly, crosslinked fibers are advantageouslyincorporated into absorbent products to enhance their wet bulk andliquid acquisition rate and to also reduce rewet.

Some of the first crosslinked cellulosic fibers were prepared bytreating cellulosic fibers with formaldehyde and various formaldehydeaddition products. See, for example, U.S. Pat. No. 3,224,926; U.S. Pat.No. 3,241,553; U.S. Pat. No. 3,932,209; U.S. Pat. No. 4,035,147; andU.S. Pat. No. 3,756,913. Unfortunately, the irritating effect offormaldehyde vapor on the eyes and skin is a marked disadvantage of thefibers. In addition, such crosslinked fibers typically exhibitobjectionable odor and have low fiber brightness.

Alternatives to formaldehyde and formaldehyde addition productcrosslinking agents have been developed. Among these are dialdehydecrosslinking agents. See, for example, U.S. Pat. No. 4,822,453, whichdescribes absorbent structures containing individualized, crosslinkedfibers, wherein the crosslinking agent is selected from the groupconsisting of C₂-C₉ dialdehydes, with glutaraldehyde being preferred.The reference appears to overcome many of the disadvantages associatedwith formaldehyde and/or formaldehyde addition products. However, thecost associated with producing fibers crosslinked with dialdehydecrosslinking agents such as glutaraldehyde is considered too high toresult in significant commercial success. Therefore, further effortshave been made to find cellulosic fiber crosslinking agents that areboth safe for use on the human skin, have good aesthetics (low odor andhigh fiber brightness), and are commercially feasible.

Polycarboxylic acids have been used to crosslink cellulosic fibers. See,for example, U.S. Pat. No. 5,137,537; U.S. Pat. No. 5,183,707; and U.S.Pat. No. 5,190,563. These references describe absorbent structurescontaining individualized cellulosic fibers crosslinked with a C₂-C₉polycarboxylic acid. The ester crosslink bonds formed by thepolycarboxylic acid crosslinking agents differ from the acetal crosslinkbonds that result from the mono- and di-aldehyde crosslinking agents.Absorbent structures made from these individualized, ester-crosslinkedfibers exhibit increased dry and wet resilience and have improvedresponsiveness to wetting relative to structures containinguncrosslinked fibers. Furthermore, the preferred polycarboxyliccrosslinking agent, citric acid, is available in large quantities atrelatively low prices making it commercially competitive withformaldehyde and formaldehyde addition products. Unfortunately, thepreferred C₂-C₉ crosslinking agent, citric acid, can cause discoloring(i.e., yellowing) of the white cellulosic fibers when treated atelevated temperatures required for crosslinking. In addition, unpleasantodors can also be associated with the use of α-hydroxy carboxylic acidssuch as citric acid. The above-noted references do not describeprocesses that reduce the odor or increase the brightness of the treatedfibers.

More recently, it was found that the characteristic odor associated withcitric acid crosslinked cellulosic fibers could be removed and thebrightness improved by contacting the fibers with an alkaline solution(e.g., an aqueous solution of sodium hydroxide) and an oxidizingbleaching agent (e.g., hydrogen peroxide). See U.S. Pat. No. 5,562,740.In the method, the alkaline solution raises the finished fiber pHpreferably to the 5.5-6.5 range from about 4.5. This in combination withthe oxidizing bleaching agent eliminates the “smokey and burnt” odorcharacteristics of the crosslinked fibers. The oxidizing bleaching agentwhen added at high consistency increases the final product brightness to80 to 86 from 70 to 75 and reduces odor.

Although some disadvantages related to brightness and color associatedwith crosslinked cellulosic fibers have been addressed, a need remainsfor cellulosic fibers having the advantages of bulk, liquid acquisition,and rewet associated with crosslinked cellulosic fibers without thedisadvantages related to diminished fiber brightness and color. Thepresent invention seeks to fulfill these needs and provides furtherrelated advantages.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides individualized cellulosicfibers having improved brightness and color. The cellulosic fibers ofthe invention are intrafiber crosslinked cellulosic fibers obtainablefrom cellulosic fibers by treatment with glyoxal. The cellulosic fibersof the invention are crosslinked by treatment with only an aqueousglyoxal solution (e.g., without a crosslinking catalyst). The fibers ofthe present invention have a brightness greater than about 80% ISO andcolor characterized by an L value greater than about 92 and a b valueless than about 7.5.

In another aspect of the invention, methods for the preparation ofcellulosic fibers having improved brightness and color are provided. Inthe methods, a fibrous web of cellulosic fibers is treated with only anaqueous glyoxal solution (e.g., without a crosslinking catalyst), wetfiberized, and then dried and cured to provide individualized cellulosicfibers having improved brightness and color.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides cellulosic fibers having improvedbrightness and color and methods for their preparation. The fibers ofthe invention are glyoxal crosslinked cellulosic fibers. The glyoxalcrosslinked cellulosic fibers are intrafiber crosslinked fibers. Theglyoxal crosslinked cellulosic fibers are made by treatment with anamount of glyoxal effective to provide crosslinked fibers having abrightness greater than about 80% ISO. The glyoxal crosslinkedcellulosic fibers have a color characterized by an L value greater thanabout 92, an a value greater than about −2.3 and less than about +0.2,and a b value less than about 7.5.

As used herein, the term “glyoxal crosslinked cellulosic fibers” refersto cellulosic fibers obtainable from cellulose fibers by treatment withan aqueous glyoxal solution without the use of a crosslinking catalyst.The glyoxal crosslinked cellulosic fibers of the invention are made bytreating a mat or web of cellulosic fibers with an aqueous glyoxalsolution to provide glyoxal treated fibers, which are then separatedinto individual glyoxal treated fibers, and heated for a time and at atemperature to effect curing (i.e., to provide glyoxal crosslinkedcellulosic fibers). The glyoxal crosslinked fibers of the invention aremade by treatment with an aqueous glyoxal solution without the use of acrosslinking catalyst. Representative methods for making the glyoxalcrosslinked cellulosic fibers of the invention are described in Example1.

As used herein, the term “brightness” refers to the reflectance of bluelight corresponding to a centroid wavelength of 457 nm in terms of theperfect reflecting diffuser (perfect reflecting diffuser is the idealreflecting surface that neither absorbs nor transmits light, butreflects diffusely, with the radiance of the reflecting surface beingthe same for all reflecting angles, regardless of the angulardistribution of the incident light). Brightness was measured accordingto TAPPI T 525 om-02 on a Technibrite MicroTB-1C instrument (TechnydineCorp.).

In one embodiment, the glyoxal crosslinked fibers have a brightnessgreater than about 75% ISO. In another embodiment, the glyoxalcrosslinked fibers have a brightness greater than about 80% ISO. Inanother embodiment, the glyoxal crosslinked fibers have a brightnessgreater than about 85% ISO. The brightness of representative glyoxalcrosslinked cellulosic fibers of the invention as a function ofcrosslinking time and temperature is presented in Tables 1 and 2.

In addition to high brightness, the glyoxal crosslinked fibers of theinvention advantageous exhibit improved color properties as indicated bythe Opponent colors scales (L, a, b), and Whiteness index (WI_(CDM-L))values. L, a and b are used to designate measured values of threeattributes of surface-color appearance as follows: L representslightness, increasing from zero for black to 100 for perfect white; arepresents redness when positive, greenness when negative, and zero forgray; and b represents yellowness when positive, blueness when negative,and zero for gray. The concept of opponent colors was proposed by Heringin 1878. Starting in 1940s, a number of measurable L, a, b dimensionshave been defined by equations relating them to the basic CIE XYZtristimulus quantities defined in CIE Document No. 15. Measured valuesfor a given color will depend on color space in which they are expressed[(TAPPI T 1213 sp-98 “Optical measurements terminology (related toappearance evaluation of paper”)].

In one embodiment, the glyoxal crosslinked fibers have a colorcharacterized by an L value greater than about 92, an a value greaterthan about −2.3 and less than about +0.2, and a b value less than about7.5, and a Whiteness Index from about 72 to about 86. In one embodiment,the glyoxal crosslinked fibers have a color characterized by an L valuegreater than about 95. The color properties of representative glyoxalcrosslinked cellulosic of the invention are provided in Tables 1 and 2.Whiteness Index (WI) is determined using a color difference meter (CDM)and is defined as:WI _({CDM-I}) =L−3b.

Basic color measurement is made using commercially available instruments(e.g., Technibrite MicroTB-1C, Technydine Corp.). The instrument scansthrough the brightness and color filters. Fifty readings are taken ateach filter position and averaged and the resulting values are printedout as Brightness, R(X), R(Y), and R(Z). Brightness is ISO brightness(457 nm), R(X) is absolute red reflectance (595 nm), R(Y) is absolutegreen reflectance (557 nm), and R(Z) is absolute blue reflectance (455nm). The CE tristimulus functions X, Y, and Z are then computed inaccordance with the following equations: X=0.782 R(X)+0.198 R(Z);Y═R(Y); and Z=1.181 R(Z). Next L, a and b values are computed using theestablished equations (Technibrite Micro TB-IC Instruction Manual TTM575-08, Oct. 30, 1989). WI_((CDM-L)) was calculated according to theequation: WI_((CDM-L))=L−3b, according to TAPPI T 1216 sp-98 (TAPPI T1216 sp-98 “Indices for whiteness, yellowness, brightness and luminousreflectance factor”).

To further illustrate the principles of the invention, a discussion ofwhiteness and brightness is useful. Webster's Dictionary defines whiteas “the object color of greatest lightness characteristically perceivedto belong to objects that reflect diffusely nearly all incident energythroughout the visible spectrum”. Used as a noun or adjective, white isdefined as “free from color”. Most natural and many man-made productsare never “free from color”. Whether the “white” product is fluff pulp,paper, textiles, plastics, or teeth, there is usually an intrinsiccolor, other than white, associated with it. Consider two hypotheticalobjects, the first that meets Webster's definition of white: onecharacterized by a flat spectrum of high reflectance and a second, whichis the first with a small amount of blue colorant added (results in anunequal spectrum). Most people will judge the second as being the whiterof the two even though its total reflectance is lower in certainspectral regions. The first will be judged as a “yellow-white” while thesecond a “blue-white”. Human color vision is more than just a sensation.It is also quite subjective and certain associations are unconsciouslymade. Blue-white is associated with “clean and pure”, while“yellow-white” denotes “dirty, old or impure”. The type and amounts offillers and colorants to use, which hues are appropriate (e.g.,red-blue, green-blue), and the optimal optical prescription to targethave been the subject of considerable interest.

The preparation of cellulosic fibers crosslinked with glyoxal using acrosslinking catalyst is described in Example 2. The crosslinkingprocedure described in Example 2 is as described in Example 1 of U.S.Pat. No. 4,888,093, Individualized Crosslinked-Fibers and Process forMaking Said Fibers. The crosslinked cellulosic fibers prepared asdescribed in Example 2 had a brightness significantly lower than thebrightness of the glyoxal crosslinked fibers of the invention. Incontrast to the glyoxal crosslinked cellulosic fibers of the inventionhaving a brightness greater than about 80% ISO, the highest brightnessachieved for the fibers crosslinked with glyoxal and crosslinkingcatalyst was about 74% ISO.

In another aspect, the present invention provides a method for makingcellulosic fibers crosslinked by treatment with an aqueous glyoxalsolution without the use of a crosslinking catalyst. In the method,cellulosic fibers are treated with an effective amount of glyoxal toachieve the brightness and color enhancements described herein.Generally, the fibers are treated with from about 0.5 to about 5 percentby weight glyoxal based on the total weight of the treated fibers. Inone embodiment, the fibers are treated with from about 1 to about 4percent by weight based on the weight of fibers.

In general, the cellulose fibers of the present invention may beprepared by a system and apparatus as described in U.S. Pat. No.5,447,977 to Young, Sr. et al., which is incorporated herein byreference in its entirety. Briefly, the fibers are prepared by a systemand apparatus that includes a conveying device for transporting a mat orweb of cellulose fibers through a fiber treatment zone; an applicatorfor applying a treatment substance such as an aqueous glyoxal solutionfrom a source to the fibers at the fiber treatment zone; a fiberizer forseparating the individual cellulose fibers comprising the mat to form afiber output comprised of substantially unbroken and essentiallysingulated cellulose fibers; a dryer coupled to the fiberizer for flashevaporating residual moisture; and a controlled temperature zone foradditional heating of fibers and an oven for curing the crosslinkingagent, to form dried and cured individualized crosslinked fibers.

As used herein, the term “mat” refers to any nonwoven sheet structurecomprising cellulose fibers or other fibers that are not covalentlybound together. The fibers include fibers obtained from wood pulp orother sources including cotton rag, hemp, grasses, cane, husks,cornstalks, or other suitable sources of cellulose fibers that may belaid into a sheet. The mat of cellulose fibers is preferably in anextended sheet form, and may be one of a number of baled sheets ofdiscrete size or may be a continuous roll.

Each mat of cellulose fibers is transported by a conveying device, forexample, a conveyor belt or a series of driven rollers. The conveyingdevice carries the mats through the fiber treatment zone.

At the fiber treatment zone, an aqueous glyoxal solution is applied tothe cellulose fibers. The crosslinking solution is preferably applied toone or both surfaces of the mat using any one of a variety of methodsknown in the art, including spraying, rolling, or dipping. Once theglyoxal solution has been applied to the mat, the crosslinking solutionmay be uniformly distributed through the mat, for example, by passingthe mat through a pair of rollers.

After the fibers have been treated with the crosslinking agent, theimpregnated mat is fiberized by feeding the mat through a hammermill.The hammermill serves to disintegrate the mat into its componentindividual cellulose fibers, which are then air conveyed through adrying unit to remove the residual moisture. In a preferred embodiment,the fibrous mat is wet fiberized.

The pulp is then air conveyed through an additional heating zone tobring the temperature of the pulp to the cure temperature. The curetemperature for glyoxal is about 150° C. In one embodiment, the dryercomprises a first drying zone for receiving the fibers and for removingresidual moisture from the fibers via a flash-drying method, and asecond heating zone for curing the crosslinking agent. Alternatively, inanother embodiment, the treated fibers are blown through a flash-dryerto remove residual moisture, heated to a curing temperature, and thentransferred to an oven where the treated fibers are subsequently cured.Overall, the treated fibers are dried and then cured for a sufficienttime and at a sufficient temperature to effect crosslinking. Typically,the fibers are oven-dried and cured for about 1 to about 20 minutes at atemperature from about 120° C. to about 165° C.

As noted above, the present invention relates to crosslinked cellulosefibers. Although available from other sources, cellulosic fibers usefulfor making glyoxal crosslinked cellulosic fibers of the invention arederived primarily from wood pulp. Suitable wood pulp fibers for use withthe invention can be obtained from well-known chemical processes such asthe kraft and sulfite processes, with or without subsequent bleaching.The pulp fibers may also be processed by thermomechanical,chemithermomechanical methods, or combinations thereof. The preferredpulp fiber is produced by chemical methods. Ground wood fibers, recycledor secondary wood pulp fibers, and bleached and unbleached wood pulpfibers can be used. The preferred starting material is prepared fromlong-fiber coniferous wood species, such as southern pine, Douglas fir,spruce, and hemlock. Details of the production of wood pulp fibers arewell-known to those skilled in the art. These fibers are commerciallyavailable from a number of companies, including Weyerhaeuser Company.For example, suitable cellulose fibers produced from southern pine thatare usable with the present invention are available from WeyerhaeuserCompany under the designations CF416, CF405, NF405, PL416, FR416, FR516,and NB416.

The wood pulp fibers useful in the present invention can also bepretreated prior to use with the present invention. This pretreatmentmay include physical treatment, such as subjecting the fibers to steamor chemical treatment. Although not to be construed as a limitation,examples of pretreating fibers include the application of fireretardants to the fibers, and surfactants or other liquids, such assolvents, which modify the surface chemistry of the fibers. Otherpretreatments include incorporation of antimicrobials, pigments, anddensification or softening agents. Fibers pretreated with otherchemicals, such as thermoplastic and thermosetting resins also may beused. Combinations of pretreatments also may be employed.

Method for determining fiber brightness. The brightness (% ISO) ofcellulosic fibers crosslinked with glyoxal of the invention wasdetermined by TAPPI T 525 om-02.

The brightness, L, a, b, and WI values of representative glyoxalcrosslinked fibers of the invention as a function of glyoxal addition,cure temperature, and cure time are summarized in Tables 1 and 2. TABLE1 Brightness, L, a, b, and WI for Representative Glyoxal CrosslinkedFibers. Cure Cure Glyoxal Temp. Time Brightness (%) (° C.) (min.) (%ISO) L a b WI_((CDM-L)) 1 150 5 84.2 95.3 −0.52 5.16 79.8 1 150 7 82.394.6 −0.57 5.71 77.5 2 130 3 87.4 95.9 −0.66 3.50 85.4 2 130 5 87.0 95.9−0.70 3.78 84.5 2 130 7 86.0 95.7 −0.76 4.22 83.0 2 140 3 87.6 96.2−0.71 3.75 84.9 2 140 5 85.1 95.6 −0.80 4.90 80.9 2 140 7 84.5 95.4−0.72 5.00 83.0 2 150 3 86.0 95.8 −0.71 4.39 82.6 2 150 5 82.8 94.7−0.75 5.44 78.4 2 150 5 83.2 95.1 −0.71 5.62 78.3 2 150 7 82.6 95.0−0.69 5.90 77.3 2.5 130 3 87.2 95.9 −0.67 3.60 85.1 2.5 130 5 87.0 95.8−0.73 3.76 84.6 2.5 130 7 86.8 96.0 −0.72 4.08 83.7 2.5 140 3 86.9 95.8−0.75 3.76 84.5 2.5 140 5 86.7 96.1 −0.82 4.26 83.3 2.5 140 7 84.7 95.6−0.75 5.09 83.7 2.5 150 3 86.9 95.9 −0.73 3.85 84.3 2.5 150 5 83.6 94.3−0.76 4.97 80.0 2.5 150 7 80.7 94.9 −0.75 6.41 75.1 3 130 3 87.5 96.0−0.71 3.62 85.2 3 130 5 87.8 96.1 −0.71 3.53 85.6 3 130 7 86.7 96.0−0.77 4.25 83.3 3 140 3 87.4 96.0 −0.74 3.71 84.9 3 140 5 86.2 96.0−0.81 4.55 82.3 3 140 7 86.2 95.8 −0.72 4.26 83.3 3 150 3 86.3 95.9−0.77 4.45 82.6 3 150 5 83.6 95.2 −0.67 5.58 78.5 3 150 5 83.4 95.4−0.81 5.90 77.7 3 150 7 80.1 94.6 −0.48 7.26 72.8 3 150 7 81.2 94.7−0.82 6.58 75.0 3.5 130 3 87.7 96.0 −0.73 3.44 85.7 3.5 130 5 87.7 96.2−0.76 3.77 84.9 3.5 130 7 86.8 96.0 −0.77 4.16 83.5 3.5 140 3 87.6 96.2−0.75 3.86 84.7 3.5 140 5 85.8 95.7 −0.84 4.41 82.5 3.5 140 7 85.2 95.7−0.82 4.96 83.5 3.5 150 3 85.7 95.8 −0.80 4.66 81.8 3.5 150 5 82.8 95.3−0.80 6.15 76.8 3.5 150 7 81.9 94.9 −0.79 6.32 76.0 4 130 3 87.6 95.9−0.69 3.37 85.8 4 130 5 88.0 96.3 −0.69 3.60 85.5 4 130 7 87.3 96.1−0.76 3.95 84.2 4 140 3 88.0 96.3 −0.73 3.61 85.5 4 140 5 86.8 96.1−0.82 4.23 83.4 4 140 7 85.3 95.8 −0.82 4.97 84.2 4 150 3 87.3 96.2−0.77 3.97 84.2 4 150 5 83.3 94.8 −0.78 5.18 79.3 4 150 5 84.5 95.7−0.89 5.36 79.6 4 150 7 83.4 95.3 −0.76 5.65 78.3 5 130 7 80.6 94.7−0.69 7.10 73.4 5 150 5 83.8 95.5 −0.69 5.78 78.1

TABLE 2 Brightness, L, a, b, and WI Values for Representative GlyoxalCrosslinked Fibers. Cure Cure Glyoxal Temp. Time Brightness (%) (° C.)(min.) (% ISO) L a b WI_((CDM-L)) 2 141 3 87.3 96.2 −0.62 4.04 84.1 2141 5 86.3 96.0 −0.62 4.54 82.4 2 141 7 84.5 95.5 −0.60 5.29 79.6 2 1493 86.5 96.0 −0.64 4.41 82.8 2 149 5 84.0 95.4 −0.56 5.49 78.9 2 149 780.5 94.5 −0.36 6.82 74.0 2 157 3 83.7 95.3 −0.55 5.63 78.4 2 157 5 80.994.6 −0.39 6.71 74.5 2 157 7 74.3 92.6 0.01 8.99 65.6 3 141 3 87.2 96.1−0.64 4.05 84.0 3 141 5 85.8 95.8 −0.65 4.68 81.8 3 141 7 84.0 95.4−0.64 5.40 79.2 3 149 3 85.9 95.7 −0.69 4.43 82.4 3 149 5 84.3 95.4−0.63 5.31 79.5 3 149 7 81.6 94.8 −0.51 6.38 75.7 3 157 3 83.0 95.2−0.66 5.88 77.6 3 157 5 79.0 94.1 −0.47 7.45 71.8 3 157 7 72.8 92.1−0.03 9.50 63.6

The present invention provides cellulosic fibers having improvedbrightness and color. The fibers of the invention are intrafibercrosslinked cellulosic fibers obtainable from cellulosic fibers bytreatment with an aqueous glyoxal solution. The crosslinked fibers canbe formed from cellulosic fibers by treatment with an amount of glyoxalwithout the use of a crosslinking catalyst effective to provide thebrightness and color enhancement described herein.

The glyoxal crosslinked cellulosic fibers of the present invention canbe advantageously incorporated into an absorbent product. Such productscan further include other fibers such as fluff pulp fibers, syntheticfibers, other crosslinked fibers, and absorbent materials such assuperabsorbent polymeric materials. Representative absorbent productsthat can include the fibers of the invention include infant diapers,adult incontinence products, and feminine hygiene products. The fiberscan be included in liquid acquisition, distribution, or storage layers.The glyoxal crosslinked cellulosic fibers of the present invention canbe advantageously incorporated into tissue and towel products.

The fibers of the invention can be advantageously incorporated intopaperboard products, including single and multi-ply paperboard products.Paperboard products that include the fibers can be used in insulationapplications, for example, insulated cups and containers. Paperboardproducts that include the fibers can also be used as packagingmaterials.

The glyoxal crosslinked cellulosic fibers of the invention areessentially odorless. This is in contrast to cellulosic fibers that havebeen modified with polycarboxylic acid crosslinking agents such ascitric acid crosslinked cellulosic fibers.

The following examples are for the purposes of illustrating, notlimiting, the present invention.

EXAMPLES Example 1 Representative Glyoxal Crosslinked Cellulosic Fibers

In this example, methods for forming representative high bulk fibers inaccordance with the present invention are described.

Method A. A selected amount of glyoxal (CARTABOND GHF containing 40percent by weight glyoxal in water) was applied to both sides of atwenty gram pulp sheet (CF416, dried wood pulp fibers available fromWeyerhaeuser Co.) using a 5 mL disposable syringe and 23.1 gauge needle.The sample was held in a resealable plastic bag for 16-18 hours at roomtemperature, then broken into pieces (e.g., about 2×2 cm), passedthrough a laboratory fiberizer, and collected as a loose pad. The padwas broken into small pieces (e.g., about 3×3 cm), placed into a screenbasket and cured at a fixed temperature and time in a Despatch V Seriesoven.

Glyoxal crosslinked fibers prepared by this method have the brightness,L, a, b, and WI values described in Table 1.

Method B. Pulp sheets in roll form (CF416, dried wood pulp fibersavailable from Weyerhaeuser Co.) were treated with glyoxal (commerciallyavailable under the designation CARTABOND GHF from Clariant Corp.)according to the following procedure. The pulp sheet was fed from theroll through a constantly replenished bath of the crosslinking solution(i.e., an aqueous solution containing a glyoxal concentration determinedby the weight add-on desired), then through a roll nip set to removesufficient solution so that the pulp sheet after treating was at about40% moisture content. The concentration of the bath was adjusted toachieve the desired level of chemical addition to the pulp sheet. Afterthe roll nip, the wet sheet was fed through a hammer mill to fiberizethe pulp. The individualized fibers were then blown through a flashdryer to affect drying and then to a cyclone where the treated cellulosefluff was separated from the air stream. The pulp was air conveyedthrough an additional heating zone to bring the temperature of the pulpto the cure temperature and then transferred to an oven where thetreated fibers were subsequently cured.

Glyoxal crosslinked fibers prepared by this method have the brightness,L, a, b, and WI values described in Table 2.

Example 2 Comparative Example Brightness and Color for Cellulose FibersCrosslinked with Glyoxal Using Catalyst

In this example, the brightness and color of cellulose fiberscrosslinked with glyoxal and catalyst is described. Wood pulp fibers(never-dried FR416, available from Weyerhaeuser Co.) were treated withglyoxal and crosslinking catalyst, zinc nitrate hexahydrate, 30 weightpercent based on the weight of glyoxal, according to the proceduredescribed in U.S. Pat. No. 4,888,093, Individualized Crosslinked-Fibersand Process for Making Said Fibers, Example 1. The only difference wasthat only one of the solutions was adjusted to 3.7 because all otherswere below this value.

The fibers were treated with glyoxal (3, 6, and 9 weight percent) andcatalyst and then cured (145° C., 45 min) to provide glyoxal crosslinkedfibers. The brightness (% ISO) and color (L, a, b, and WI) values forthe glyoxal crosslinked fibers is summarized in Table 3. TABLE 3Brightness, L, a, b, and WI for Glyoxal/Catalyst Crosslinked Fibers CureCure Glyoxal Temp. Time Brightness (%) (° C.) (min.) (% ISO) L a bWI_((CDM-L)) 3 145 45 73.2 92.5 −0.59 9.54 63.9 6 145 45 65.6 90.3 −0.3112.81 51.8  6* 145 45 67.4 90.3 −0.23 11.43 56.0 9 145 45 60.6 88.0 0.0613.89 46.3*pH was adjusted to 3.7 (as specified in the '093 patent). The pH of theother three samples remained ‘as-is’, 2.74, 2.50, and 2.27 for 3, 6, 9wt % glyoxal, respectively.

As shown in Table 3, brightness and L decrease with increasing glyoxalamount, and b increases with increasing glyoxal amount.

While the preferred embodiment of the invention has been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.

1. Individualized, crosslinked cellulosic fibers, comprising cellulosicfibers treated with only an aqueous glyoxal solution in an amounteffective to provide crosslinked fibers having color characterized by anL value greater than about
 92. 2. The fibers of claim 1 having an avalue greater than about −2.3 and less than about +0.2.
 3. The fibers ofclaim 1 having a b value less than about 7.5.
 4. The fibers of claim 1,wherein the L value is greater than about
 95. 5. The fibers of claim 1having a brightness greater than about 80% ISO.
 6. The fibers of claim 1having a brightness greater than about 85% ISO.
 7. The fibers of claim1, wherein the amount of glyoxal is from about 0.5 to about 5 percent byweight based on the weight of fibers.
 8. The fibers of claim 1, whereinthe amount of glyoxal is from about 1 to about 4 percent by weight basedon the weight of fibers.
 9. An absorbent product, comprising cellulosicfibers treated with only an aqueous glyoxal solution in an amounteffective to provide crosslinked fibers having color characterized by anL value greater than about
 92. 10. The product of claim 9, wherein thecrosslinked fibers have a brightness greater than about 80% ISO.
 11. Theproduct of claim 9 further comprising fluff pulp fibers.
 12. The productof claim 9 further comprising superabsorbent material.
 13. The productof claim 9, wherein the product is an infant diaper.
 14. The product ofclaim 9, wherein the product is an adult incontinence product.
 15. Theproduct of claim 9, wherein the product is a feminine hygiene product.16. The product of claim 9, wherein the product is at least one of atissue or towel.
 17. A paperboard product, comprising cellulosic fiberstreated with only an aqueous glyoxal solution in an amount effective toprovide crosslinked fibers having color characterized by an L valuegreater than about
 92. 18. The product of claim 17, wherein thecrosslinked fibers have a brightness greater than about 80% ISO.
 19. Theproduct of claim 17, wherein the product is an insulated paperboard. 20.The product of claim 17, wherein the product is a packaging material.